Current analyzers, as are used as a matter of routine in analytics, forensics, microbiology and clinical diagnostics, are able to carry out a multiplicity of detection reactions and analyses with a multiplicity of samples. In order to be able to carry out a multiplicity of examinations in an automated manner, various automatically operating devices for the spatial transfer of measuring cells, reaction containers and reagent liquid containers are required, such as transfer arms with a gripper function, transport belts or rotatable transport wheels, and devices for transferring liquids, such as pipetting devices. The analyzers comprise a central control unit which, by means of appropriate software, is able to largely independently plan and work through the work steps for the desired analyses.
Many of the analysis methods used in such analyzers operating in an automated manner are based on optical methods. Measurement systems based on photometric (e.g., turbidimetric, nephelometric, fluorometric, or luminometric) or radiometric measurement principles are particularly widespread. These methods permit the qualitative and quantitative detection of analytes in liquid samples without having to provide additional separation steps. The determination of clinically relevant parameters, for example, the concentration or the activity of an analyte, is often implemented by means of an aliquot of a bodily fluid of a patient being mixed simultaneously or in succession with one or more reagent liquids in a reaction vessel, as a result of which a biochemical reaction is set in motion, which brings about a measurable change in an optical property of the test preparation.
The measurement result is in turn forwarded to a memory unit by the measurement system and evaluated. Subsequently, the analyzer supplies a user with sample-specific measurement values by way of an output medium, such as a monitor, a printer, or a network connection.
For the spatial transfer of liquid containers, clamping grippers for grasping, holding, and releasing a liquid container are often provided, the clamping grippers being secured, by way of a flexible connecting element, on a horizontally and vertically movable transfer arm. EP-A2-2308588 describes an example of a device for transferring tube-shaped reaction vessels (cuvettes) within an automated analyzer. The device comprises a passive, elastically deformable gripper with two gripper arms for force-fit capture and holding of a liquid container and is suitable for receiving an individual cuvette placed in a receiving position, transporting the cuvette to a target position, and setting it down there in a further receiving position. Compared to active mechanical grippers, passive clamping grippers of this kind have the advantage of being relatively robust, by virtue of their simple design, and of requiring minimal maintenance.
The transport, described in EP-A2-2308588, of a liquid container with the clamping gripper basically comprises the following steps:
a) moving the clamping gripper horizontally in order to produce a clamped connection between the clamping gripper and the liquid container in a start position;
b) raising the clamping gripper in order to remove the liquid container from the start position;
c) moving the clamping gripper horizontally to a target position;
d) lowering the clamping gripper in order to position the liquid container in the target position; and
e) moving the clamping gripper horizontally in order to release the clamped connection.
To receive or in other words take hold of a liquid container that stands upright in a receiving position (start position), the clamping gripper is moved laterally onto the liquid container by a horizontal movement of the transfer arm and is pressed against the liquid container until the clamping gripper opens and encloses the liquid container with force-fit engagement. By means of an upward movement of the transfer arm, the liquid container held by the clamping gripper is raised from the receiving position and can now be transported to any given target position in the analyzer, for example, to a receiving position in a measuring station. To set down or in other words release the liquid container in the target position, the liquid container is first of all lowered to the receiving position by a downward movement of the transfer arm, and the clamping gripper is drawn away laterally from the liquid container by a horizontal movement of the transfer arm. In this way, the liquid container is pressed against the inside wall of the receiving position and exerts a force on the clamping gripper, which finally opens and releases the liquid container.
A problem is that, when the cuvette is being received and being released, the lateral pressing on or pulling away of the gripper can have the effect that liquid splashes out of the cuvette, because the cuvette, during the pressing on or pulling away of the gripper, can at first tilt slightly in the receiving position and, when the gripper opens with a snap movement, is accelerated counter to the direction of travel of the gripper and strikes against the inside wall of the receiving position. Splashing liquid in the analyzer can lead to loss of liquid volume, to sensitive components being damaged, to liquid splashing into adjacent sample vessels or reaction vessels, thus causing distortion of measurement results, and also increased risk of infection of a user, particularly if the splashing liquid contains human or animal bodily fluids such as blood or urine.
To avoid such disturbances, the use of active gripper systems is known. U.S. Pat. No. 5,772,962 describes a gripping device with two gripper arms which are connected to each other via a tension spring. Moreover, an expansion device is provided which is able to press the gripper arms away from each other and thus control the gripping mechanism.
However, a disadvantage of active gripper systems is the high level of maintenance required, since the hundreds or even thousands of uses daily leads to rapid wear of the mechanical parts.